The present invention relates to a starting motor, and particularly to a technique suitable for preventing a starting motor from resulting in a thermal breakdown.
Generally, when a starting motor receives continuous energization for starting engine or intermittent energization for a short time of cycle, self heat generation of an energization part increases, so that a part of which self heat generation is greater than radiation accumulates heat and the heat accumulating part itself or a part which receives radiant heat of the heat accumulating part assumes an abnormally high temperature, resulting in a thermal breakdown of a combustible substance of the part mentioned above.
As the procedure to prevent such a phenomenon as described, there is a prior art which have a construction in which a xe2x80x9cfusexe2x80x9d is installed in a driving circuit of a starting motor. By xe2x80x9cfusexe2x80x9d what is meant herein is that xe2x80x9cAn element is mounted in a circuit and blows quickly when an over load or an over current occurs.xe2x80x9d, and its fusing characteristic is generally set by xe2x80x9cover current valuexc3x97timexe2x80x9d. All the prior arts are constituted on the basis of the conception of the xe2x80x9cfusesxe2x80x9d as described above. A first prior art xe2x80x9cJapanese Utility Model Laid-Open No. 57-174760 has a construction in which a xe2x80x9cfusexe2x80x9d is provided in a motor main circuit of a starting motor, and a second prior art xe2x80x9cJapanese Patent Laid-Open No. 9-273464 has a construction in which a part of a conductor constituting a motor circuit of a starting motor has locally an increased current density, which is used in place of the xe2x80x9cfusexe2x80x9d.
However, in the starting motor, a current flowing into the motor is always varied due to the engine load torque (for example, when no load is present, approximately 100 A, and when the engine is locked, approximately 1500 A, etc.), and further, in all current areas, there is the possibility that the thermal breakdown occurs with some time, thus making very difficult to satisfy the fusing time characteristic in all the current areas by means of one fuse. (For example, in a xe2x80x9cfusexe2x80x9d whose fusing time characteristic is set by I (ampere)xc3x97T (time), there occurs a problem that the fuse does not blow when a motor current is not more than I.)
It is an object of the present invention to provide a starting motor capable of preventing the starting motor from resulting in a thermal breakdown by a small-size and simple construction and an inexpensive technique without impairing the mounting layout properties of the stating motor and the performance within the rated use.
To achieve the above-described object, there is provided a starting motor comprising a motor which is rotated by energization from a battery; a pinion to which the rotation of a motor is transmitted; a shift lever for moving the pinion to a ring gear of the engine; and an electromagnetic switch provided with a coil for inducing an electromagnetic force, an axially slidable plunger, and a contact for opening and closing energization to the motor; the starting motor comprising a circuit disconnecting part that blows on receiving radiant heat generated by heat generation of the motor circuit, the circuit disconnecting member being connected to the motor circuit and blowing at a temperature lower than a thermal breakdown temperature of a combustible substance around the motor circuit.
Preferably, there is provided the starting motor wherein a part of the motor circuit is used as the circuit disconnecting part.
More preferably, there is provided the starting motor wherein a material for a part for connecting a terminal of the contact for opening and closing energization to the motor to the motor circuit is used for the circuit disconnecting member.
More preferably, there is provided the starting motor wherein the circuit disconnecting member is installed in a battery cable and at a position which receives radiant heat generated by heat generation of the motor circuit.
More preferably, there is provided the starting motor wherein the circuit disconnecting member is installed in a key switch circuit and at a position which receives radiant heat generated by heat generation of the motor circuit.